Familial pulmonary fibrosis is indistinguishable pathologically from idiopathic pulmonary fibrosis and appears to be inherited as an autosomal dominant trait with variable penetrance; pulmonary fibrosis is associated with pleiotropic genetic disorders, such as Hermansky-Pudlak syndrome, neurofibromatosis, tuberous sclerosis, Neimann-Pick disease, Gaucher's disease, and familial hypocalciuric hypercalcemia; pulmonary fibrosis is frequently observed in autoimmune disease, including rheumatoid arthritis and systemic sclerosis; variable susceptibility is evident among workers who are reported to be exposed occupationally to similar concentrations of fibrogenic dusts; and inbred strains of mice differ in their susceptibility to fibrogenic dust.